1. Field of the Invention
The present invention relates to a slide device for a vehicle seat that moves a seat body in the front-rear direction of a vehicle body by a relative movement of an upper rail to a lower rail.
2. Description of the Related Art
A typical slide device for a vehicle seat is mainly configured with a lower rail being fixedly installed on a floor of a vehicle body and extending in the front-rear direction of the vehicle body, and an upper rail being coupled to the lower rail so as to be relatively movable and supporting a seat body.
In this type of slide device, the coupling of the upper rail to the lower rail is generally achieved by rollers that are respectively attached to front and rear portions of the upper rail and supported so as to be rollable between a bottom wall and a top wall of the lower rail. In order to ensure a smooth seat slide operation through the rolling of the rollers, outer diameters of the rollers are generally set to be smaller than a gap between the bottom wall and the top wall of the lower rail. However, a space formed thereby between the lower rail and the rollers may cause the rollers to rattle.
As a technology that ensures the smooth seat slide operation while preventing an usual sound due to the rattling of the rollers, for example, Japanese Unexamined Patent Application Publication No. 2007-69694 discloses a technology that provides sub-rollers respectively near main rollers provided on the front and rear portions of the upper rail, and biases the sub-rollers upward and abuts the sub-rollers to the top wall of the lower rail so to abut the main rollers to the bottom wall of the lower rail.
Incidentally, a slide device which supports an occupant through a seat body requires a certain supporting strength and the like. Accordingly, in order to ensure supporting strength in the slide device of this type while more reliably preventing the rattling of the upper rail and the like, it is preferable to arrange rollers not only at the front and rear portions of the upper rail but also at an intermediate position therebetween and the like as needs dictate.
However, if rollers are arranged in tandem at three or more positions on the upper rail, a smooth movement of the upper rail in the front-rear direction may be hindered when, for example, the lower rail is bent by an impact upon a vehicle frontal crash or the like. In particular, in the case of a so-called three-row seating vehicle, which has three rows of seats in a vehicle compartment in the front-rear direction, if the front-rear movement of an seat body in the second row is hindered, it may be difficult for an occupant seated in the third row to escape quickly.
In order to address this problem while ensuring a smooth seat slide operation also upon a frontal crash, the lower rail may be composed of a highly rigid material for example, but the enhancement of the rigidity of the lower rail could cause an increase in weight, a steep rise in cost, or the like.